This invention relates to needle electrodes for recording electromyographic activity and more particularly to a set of paired needle electrodes, having a fixed spaced relationship from each other, which can be separated or broken apart when desired.
Needle electrodes which can be used for recording facial electromyographic activity for the purpose of intraoperative facial nerve monitoring include surface electrodes, monopolar and concentric electromyographic needle electrodes and electroencephalographic needle electrodes as well as wire.
Recording needle electrodes may be placed in a close relationship or a relatively distant arrangement. Proponents of distantly spaced recording needle electrodes believe that such arrangement is more sensitive in representing a relatively greater amount of facial musculature. However, the relatively distant arrangement of needle electrodes is also sensitive in detecting electrical artifacts and false positive responses. Proponents of recording needle electrodes having relatively close proximity to each other such as 0.5 cm. apart, generally do not report a lack of recording sensitivity.
Standard bipolar or concentric needle electrodes and monopolar electromyographic needle electrodes are generally not as favored as electroencephalographic needle electrodes in recording facial electromyographic activity, presumably because electroencephalographic needle electrodes usually have a broader area of contact of facial musculature and generally indicate a greater overall sensitivity. However, electroencephalographic needle electrodes provide variations in signal quality, especially in cases of excessively thick skin and subcutaneous tissue over the facial muscles. This variation in signal quality may be due to significant parallel contact of the needle electrodes to inactive tissue with relatively less area of the needle electrode actually inside the facial muscle tissue.
Wire electrodes provided with needles of 1 inch to 1.5 inch length can circumvent this problem by placement o the entire contact area of the wire electrode inside the facial muscles. The length of the wire electrode used for insertion allows the wire electrode to be placed parallel to the plane of the facial muscles. Thus the chance of broad contact of the wire electrode to facial muscle is maximized. However, wire electrodes of adequate quality are not commercially available and are usually fabricated by individual practitioners. Furthermore, the delicate nature of wire electrodes is such that they are difficult to use and are often used only once.
At present there is no standard method of arranging wire leads from the needle electrode back to the patient connector box. Some practitioners use long leads while others employ short leads with harnesses that have a twisted pair arrangement of the wires in a given bipolar pair.
It is known that inadequate care in the arrangement of the low signal high impedance needle electrode leads may lead to enhanced "antenna-like" qualities of the input and result in excessive sensitivity to electrical artifacts. Thus the lack of standard methodology for facial electromyographic recording in intraoperative facial nerve monitoring can lead to disparate results and adversely affect the apparent reliability of the technique and/or equipment associated with such recording.
It is thus desirable to provide an intramuscular facial nerve recording needle electrode which is simple to use and permits reliable placement yet provides high quality and sensitive recording of facial electromyographic activity. It is also desirable that the needle electrode permit ease of insertion, have the requisite sensitivity, be reusable and provide high quality recorded signals that are available with wire electrodes.